Method of pumping liquid oxygen



1949- v c. R. ANDERSON 2,480,094

METHOD OF PUMPING LIQUID OXYGEN Filed July 16, 1945 2 Sheets-Sheet l 3 \l J Q F INVENTOR. Car/ 1? Andaman [-2 BY g;

Aug. 23, 1949. c. R. ANDERSON METHOD OF PUMPING LIQUID OXYGEN 2 Sheets-Sheet 2 Filed July 16, 1945 INVENTOR. Car/ 6. Anderson a wf mama Aug. 23, 1949 Carl anneal-son,

chamniitga, Tenniiassignor to Air Products, Incorporated, Chattanooga, Tenn, summation of Michigan Application July it, 1945, Serial No. 605,4 I

claim. (01. (ac-115.5)

This invention relates to a method of pumping liquefied gases.

An object of the invention is. to provide a method of withdrawing a liquefied gas from'a vessel in which it is stored or is being collected,

in such manner as to avoid the possibility of gas locking the pump. I

An object of theinvention, is to provide a method of withdrawing a stream of liquefied gas of any desired constant quantity from a collecting pool in a gas fractionating column.

An object of the invention is to provide a method of withdrawing a streamer gas from a fractionating tower and of reducing the gas to liquid form for delivery under pressure by means adapted to the pumping of liquids.

An object of the invention, method of pumping liquefied oxygen directly from a pool of commercially pure oxygen in a fractionating tower to cylinders or pipe lines inwhich gaseous oxygen is transported under high pressure, thereby avoiding the requirement for an oxygen storage tank and a gaseous oxygen compressing system.

An object of the invention is to provide a method of withdrawing oxygen in gaseous form from the pure oxygen vapor space in a fractionating tower, liquefying the gaseous stream and delivering the oxygen into pressure cylinders or pipe lines, thereby retaining in the tower any lubricating oil or other combustible substance which may enter the tower with the air stream.

While the invention is applicable to the handling of all liquefied gases (liquids having a boiling point so much below atmospheric temperature that heat leakage into insulated apparatus is likely to produce difliculties in pumping), it is found most useful in connection with the pumping of liquid oxygen because of the very low atmospheric-pressure boiling point or this liquid and the fact that the presence, in the apparatus containing the compressed gas at atmospheric temperature, of any trace of carbonaceous substances is the source of extreme danger.

The invention will therefore be described in connection with the manipulation of oxygen, it being understood that such description is illustrative and not limiting.

In the attached drawings apparatus for carrying out the invention is illustrated schematically in two modifications, to wit:

Fig, 1 illustrates a form in which oxygen is withdrawn in the liquid state from the pureoxygen pool in the base of the upper section of a double 'fractionating column and is cooled by is to provide a gen. is cooledbelow products are customarily 2 heat interchange with crude oxygen in its passage. igrom the high pressure to the low pressure stage of the column and in which the liquid 'oxyits boiling point at the pressur existing in the pump cylinderduring the suction stroke by heat interchange with gaseous product nitrogen from the low pressure stage of the column.

Fig. 2 illustratesa form withdrawn in the gaseous state from the pure oxygen pool in the base of the upper section of a double fractionatingcolumn andis condensed by heat interchange with liquid nitrogen from the'high pressure stage of the column and in in which oxygen is which the condensed oxygen is cooled below its.

boiling point at the pressure existing in thepump cylinder during the suction stroke by heat interchange with gaseous product nitrogen from the low pressure stage of the column.

The fractionating equipment illustrated is con.- ventional and any preferred form of double column may be used.

In the fractionation of air in a double column, the top products of both the high pressure and low pressure-sections are usually mixtures considerably'richer in nitrogen than is atmospheric air, rather than being pure nitrogen. These referred to as nitrogen by those versed in the art, hence in the use of the word nitrogen herein and in the claims, it is intended that its meaning shall include such nitrogen rich mixtures.

For the purpose of illustration the double column apparatus, of Figs. 1 and 2 consists essentially of a double pass heat interchanger l0, having two banksof tubes ll-l| and l2--l2, together with a fractionating column consisting of two sections l3 and I3; each provided with, a plurality of bubbling plates A and A' respectively and a boiling coil l4 in the base. Boiling coil it, although desirable, is not essential, Coil [4 may be'omittedand air passed directly from interchangerl0 through-an expansion valve 20 and into the bottom compartment of highpressure column l3,immediately above pool l8.

The flows through this system, which also are conventional, are as-follows: Air under pressure,

from a source not shown, enters the system through feed pipe l5, passes through tubes ll,

thence through pipe Hi to the boiling coil H. The upper section is provided with a condenser H, the condensate from which drains into the ll of crude (for example 95%) oxygen in the base of the lower section and thence. through pipe l9 and expansion valve 29 intothe lower section at medial height. This section fractionates the feed in the well-known manner, a gas richer in nitrogen than atmospheric -*air rising into the condenser l1, pool 2| of pure oxygen collecting in the base of the upper section. As this section is maintained at a materially lower pressure than the lower section, the condenser acts as a reboiler for the pure oxygen and returns the nitrogen rich gas as a liquid, part falling into pool 22 and part falling on to the top plate of the lower section ll. From pool 22 some of the liquid overflows and, together with that part falling directly on to the top plate from the condenser, acts as reflux in the lower section, while the remainder is transferred through pipe 23 and expansion valve 24 to the top of the upper section in which it acts as reflux. The crude oxygen is transferred through pipe 25 and expansion valve 25 to a medial point in the upper section. in which it is fractionated in the well-known manner to s'bstantially pure oxygen and slightly impure nitrogen.

At this Point we have two products-nitrogen and oxygen-each at a temperature which slightly exceeds its atmospheric pressure boiling point. These temperatures are approximately 81 Kelvin (at five pounds gauge) for nitrogen and 93 Kelvin (at six pounds gauge) for oxygen.

If these products were to be recovered as gases at atmospheric temperature and pressure, they would merely be conducted to interchanger II, the nitrogen by connecting pipe 21 to discharge directly into the interchanger and the oxygen by connecting pipe 29 to discharge directly into line 29 and hence into the interchanger, the pressures in the column being suflicient to discharge the gaseous product against frictional resistance and atmospheric pressure.

It is, however, very dasirable in many cases to conduct the oxygen product directly to the cylinders or pipe lines in which it is transported as a compressed gas, at pressures ranging up to 2500 or more pounds per square inch. Although it is common practice to bring the gaseous oxygen to substantially atmospheric temperature and pressure and to thereafter compress it, it is desirable to pump it as a liquid and to vaporize it while subjected to the pump pressure, prior to entering the pipe line or storage vessel.

An advantage in pumping the oxygen in liquid phase lies in the avoidance of use of the aqueous The step of pumping liquid oxygen has proven in practice to be one of great difliculty. The liquid is, in the nature of the case, at its boiling point at the existing pressure. From this it follows that any reduction'in pressure, such as is occasioned by fluid friction in the pump suction. or any increase in enthalpy due to leakage of heat into the pump body or to frictional heat transmitted into the liquid, will cause the evolution of gas which locks the suction and puts the pump out of commission. A further cause of vapor lock is back leakage through the discharge valve, the high pressure leakage liquid partially flashing to the gaseous state.

I have solved this problem by two steps which is immersed in a pipe 50 and suction valve 3| into with the stream of crude which are preferably used together but may be used individually. The first is to utilize a small portion of the cooling effect available in the gaseous product nitrogen for cooling the stream of liquid oxygen, on its way to the pump. to a ternperature below that corresponding to its boiling point at the pressure existing in the pump cylinder during the suction stroke. The second is to utilize another small portion of the refrigerating value of the nitrogen in cooling the pump cylinder. I

vIn the two figures of the instant application, the oxygen pump 30 may be any pump capable of handling liquid at high pressure but is here illustrated as a single acting plunger pump, having a suction valve 3|, a discharge valve 32, a cylinder II, a plunger 34, a rod 35, a crosshead 35, a connecting rod 31. a crank 38, a worm gear 35, a driving worm pinion 40 and an actuating motor 4|. 4

In the form shown in Fig.1, oxygen withdrawal pipe 28 is connected into the base of upper column section l3 at a point 42 below the liquid level of pool 2|. The oxygen thus withdrawn is cooled in interchanger 43 byv heat interchange oxygen flowing through pipe 25, interchanger 43 being downstream from expansion valve 26. The liquefied oxygen then flows through pipe 44 to interchanger 45 in which it is cooled by heat interchange with gaseous nitrogen as described below, thence through the pump cylinder on the upstroke of the plunger. On the downstroke the liquid passes through discharge valve 32 and pipe 29 to the tube bank l2 of interchanger III, in which the stream is brought to atmospheric temperature and the gaseous condition and is discharged at any desired pressure through pipe 5|. If desired, the stream in pipe 29 may be directed to a storage vessel or pipe line in liquid condition, but more usually it will be passed through the interchanger and delivered by pipe 5 l to pressure cylinders 52 or other pressure vessels or to pipe lines in which it is transported under pressure in the gaseous state.

The stream of gaseous nitrogen in pipe 21 is passed through the opposite side of interchanger 45, preferably in counter-flow to the stream of liquid oxygen, and the liquid is thus cooled to a temperature below its boiling point at column pressure.

The stream of nitrogen which, because of its relatively great mass, has been only slightly elevated in temperature, flows through pipe 45 and a coil 41 wrapped around the pump cylinder, in which it acts to withdraw any heat which might otherwise be transmitted to the liquid in the pump and tends to maintain the low temperature imparted to the liquid in interchanger 45.

From this coil the gaseous nitrogen passes through pipe 48 to the shell of interchanger ill, from which it is delivered in gaseous form and at substantially atmospheric temperature through pipe 49.

By the use of this cooling cycle, a properly designed and insulated pump may be caused to operate at full stroke capacity for extended cratin eflect which may be compensated by a corresponding adjustment in air teed pressure.

Cylinders 2 are coupled to the gaseous oxyen disch rse pipe 5| through individual valves 53 by means of which the stream of gaseous oxygen emanating from interchange! ll may be stored in synchronism with the output of the iractionating' system. The pressure maintained in oxygen bank i2--i2 oi interchanger will be equal to the momentary pressure in the cylinder being filled, plus a small pressure drop in the transmission line and valve. 4

In theiormshown in Fig. 1, it will be seen that the stream of oxygen which is drawn from the upper section of the double iractionating column is cooled by crude ongen drawn from the highest pressure stage of the column and is cooled by gaseous nitrogen drawn from the lowest pressure stage of the column.

The modification shown to eliminate any danger of oil being carried with the oxygen into the iilled cylinders or into any part of the apparatus in which detonative combustion might occur. This permits the use oi oil lubricated primary air compressors and avoids the diiliculties attendant on water or soap-water lubrication.

In the modification shown in Fig. 2, it is proposed to condense the oxygen with nitrogen drawn from the highest pressure stage of the operation and to cool gaseous nitrogen drawn from the lowest pressure stage of the operation. The crude oxygen is transferred through pipe 25 and expansion valve 28 to a medial point in the upper section II in which it is fractionatedin the well-known manher to substantially pure oxygen and slightly impure oxygen. The withdrawal of oxygen from pool ii is accomplished by the same means as described above with respect to the form shown in Fig. 1 except for that the point 42 is above the liquid level oi the oxygen in the pool.

The gas withdrawn at point '42 above pool 2! is reliquefled in condenser 43 by heat interchange with nitrogen withdrawn from pool 22 in condenser i'l. Liquid nitrogen from pool 22 is withdrawn through line 28 and expansion valve 24 and passes through condenser 43 where it condenses pure oxygen vapor. This step of condensing the gaseous oxygen has the major advantage of preventing the passage of combustible impurities into any part of the system containing compressed oxygen. The nitrogen passes into the upper portion of section I! where its liquid portion serves as reflux and where its gaseous portion joins and becomes a part oi the product nitrogen" which passes out through pipe line 2i. The gaseous product nitrogen flows through line 21 into interchanger 45 (where it sub-cools the liquid oxygen) and thence through line 48 and coil 41 (where it sub-cools pump 30) and thence through line 48 into heat interchanger l0 and thence outwardly through line 49, as described above with respect to Fig. l. The condensed oxygen from condenser 43 flows through line 44, heat interchanger 45 and by intake valve 3i into the cylinder of pump 30 from whence it is discharged as a liquid by discharge valve 32 and line 2! into tubes I! of the interchanger and thence through line Ill into cylinders 52, as in the above described form of the invention.

From the above it will be seen that the oxygen product can be withdrawn irom the column in either the liquid or the ,iorm. In the in Fig. 2 is designed the liquefied oxygen with interchange against an first alternative interchangers 43 and 4B function to cool the liquid in stages and in the second alternative interchanger 43 iunctions mainly for condensing-the gaseous oxygen and interchanger 45 functions mainly for cooling the condensed stream.

This application is a my copending application Serial No. 488,650, filed May 27, 1943.

a I claim: p

1. In the conduct of a multistage fractionating operation in which operation a mixture of com ponent gases having boiling points substantially below atmospheric temperature is compressed and cooled, the compressed and cooled mixture expanded and the eflluent of the expansion step subjected to the fractionation operation to produce a higher boiling point fraction and a lower boiling point fraction, the steps comprising:

withdrawing a stream of the higher boiling point I fraction from the low pressure stage of said operation; bringing saidstream into a first heat expanded product drawn from the highest pressure stage of said operation; reducing the temperature of said stream to a point below the boiling point of the higher boiling point fraction at the minimum momentary pressure reached in an ensuing pumping step, in a second heat interchange between said higher boiling point fraction stream and a fluid difierent from and colder than said expanded product, and pumping said higher boiling point fraction stream in substantially liquid form.

2. In the conduct of a multistage fractionating operation in which operation a mixture of component gases having boiling points substantially below atmospheric temperature is compressed and cooled, the compressed and cooled mixture expanded and the eifluent of the expansion step subjected to the fractionation operation to produce a higher boiling point fraction and a lower boiling point fraction, the steps comprising: withdrawing a stream of higher boiling point fraction vapor 'from the low pressure stage of said operation; condensing said vapor stream in a. first heat interchange against an expanded product drawn from the highest pressure stage of said operation; reducing the temperature of said condensed stream to a point below the boiling point of the higher boiling point fraction at the minimum momentary pressure reached in an ensuing pumping step, in a second heat interchange between said higher boiling point fractionstream and a fluid different from and colder.

than said expanded product, and pumping said higher boiling point fraction stream in substantially liquid form. I v

3. In the conduct of a multistage fractionating operation in which operation a mixture of component gases having boiling points substantially below atmospheric temperature is compressed and cooled, the compressed and cooled mixture expanded and the eflluent of the expansion step subjected to the fractionation operation to produce a higher boiling point fraction and a, lower boiling point fraction, the steps comprising:

. withdrawing a stream of said higher boiling point fraction from the fractlonating operation; pumping said withdrawn stream in liquid form in a manner producingrapid periodic fluctuations in pressure; cooling said stream below its original temperature and to a temperature at which the evolution of vapor from said higher boiling point traction at the minimum momentary pressure reached in said pumping step is substantially continuation-impart oi 7 avoided; and eflecting said cooling at least in part by heat interchange between said stream and an expanded product drawn from the highest pressure stage of said operation.

4. In a process involving the withdrawal of a stream of. oxygen from the low pressure stage of a multistage air fractionating operation, the steps comprising: progressively removing heat from said stream in two stages. each comprising a heat interchange between said oxygen stream and a colder fluid from said operation, in the second of which stages said colder fluid is gaseous nitrogen drawn from the low pressure stage of said operation, thereby reducing said oxygen to a temperature avoiding flashing in an ensuing pumping step, and thereafter pumping said withdrawn stream to a desired destination in liquid form.

5. In a process involving the withdrawal of a stream of oxygen from the low pressure stage of a multistage air fractionating operation, the steps comprising: bringing said stream into heat interchange relation successively with crude oxygen drawn from the highest pressure stage of said operation and with gaseous nitrogen drawn from the low pressure stage of said operation, the last said interchange reducing said oxygen to a temperature of stability in an ensuing pumping step, and pumping said withdrawn stream to a desired destination in liquid form following'last said heat interchange.

6. In a process involving the withdrawal of a stream of oxygen from the low pressure stage of a multistage air i'ractionating operation, the steps comprising: bringing said stream into heat interchange relation successively with liquid nitrogen drawn from the highest pressure stage of said operation and with gaseous nitrogen drawn from the low pressure stage of said operation, and pumping. said withdrawnstream to a desired destination in liquid form following last said heat interchange.

7. In a process involving the withdrawal of a stream of oxygen vapor from the low pressure stage of a multistage air fractionating operation, the steps comprising; condensing said vapor stream by heat interchangeagainst a stream of liquid nitrogen drawn from the highest pressure stage of said operation; further cooling said condensed stream to a temperature of stability in an ensuing pumping operation, and pumping said cooled stream in liquid form.

8. In a process involving the withdrawal of a stream of oxygen vapor from the low pressure stage of a multistage air fractionating operation,

the steps comprising: condensing said vapor stream by heat interchange against a stream of liquid nitrogen drawn from the highest pressure stage of said Operation, and cooling the condensed stream below its temperature of con- .densation and to a temperature of stability at a reduced pressure by heat interchange against a stream of gaseous nitrogen drawn from the lowest pressure stage of aid operation.

9. In a meth for producing oxygen and conditioning it for delivery to a receiving means, in which air after compression and cooling is rectifled in two stages relatively high and a relatively low pressure, in which a produce enriched in nitrogen and a product enriched in oxygen are produced in said high pressure stage and transferred to said low pressure stage and in which a cold nitrogen product and a liquid oxygen product having a temperature corresponding to its boiling point at said low pressure are produced in said low pressure stage; the set of steps comprising subjecting fluid from said oxygen product to heat exchange successively with a colder fluid derived from said high pressure stage and with a colder fluid derived i'rom said low pressure stage and thereby forming a sub-cooled liquid oxygen product;

' pumping said sub-cooled liquid oxygen product to a desired higher pressure, said sub-cooling reducing the liquid oxygen temperature at least sumciently to prevent the same from flashing into vapor during such pumping; and converting the liquid oxygen at said higher pressure into a gas by heat exchange with the compressed air to be liquefied.

10. The process of separating air into its constituents, oxygen and nitrogen, and conditioning the oxygen for delivery into a receiving system, said process comprising compressing and subjecting the air to a refrigerating eiiect at relatively high pressures, subjecting said air to a, fractionation .at relatively high pressure into two portions, one rich in oxygen and the other rich in nitrogen, subsequently rectifying said portions at a relatively low pressure to produce separate fractions, one consisting essentially of oxygen and the other consisting essentially of nitrogen, withdrawing oxygen from said one fraction in the gaseous phase and submitting it to a condensing operation by heat exchange with a colder product developed in said high pressure fractionation, withdrawing liquid oxygen from the condensing operation, sub-cooling the withdrawn liquid by heat exchange with the nitrogen product of said rectification, pumping the liquid oxygen to a relatively high pressure, using the cold of the liquid oxygen at high pressure to produce said refrigerating eflect and thereby vaporizing the-oxysen.

CARL R. ANDERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS maintained respectively at a 

